Inorganic glasses conventionally employed in the fabrication of lenses for ophthalmic applications exhibit relatively high density. This density can result in some discomfort to the wearer of eyeglasses, particularly to the wearer of lenses having a high power prescription. Organic plastics used in the fabrication of ophthalmic lenses exhibit relatively low densities, but are inferior to glass lenses with respect to hardness and scratch resistance. Furthermore, no organic photochromic material has been developed which is not subject to fatigue; i.e., the organic photochromic materials quickly lose their capability of reversibly darkening. Therefore, both from the desire to reduce the weight of the lenses and the desire to fabricate lenses demonstrating photochromic behavior, considerable research has been conducted to prepare glass/plastic composite lenses.
One such line of research has involved the incorporation of glass particles into a matrix of an organic plastic. An example of that research is illustrated in U.S. Pat. No. 4,581,288. However, total avoidance of light scatter and distortion has been difficult to achieve in that practice.
Much more extensive research has been directed to lenses having a laminated structure. Hence, the patent literature is replete with disclosures of composite lense consisting of one or more glass laminae with one or more plastic laminae. Some of those disclosures describe products wherein the glass and plastic laminae are bonded directly to one another. In other structures the glass and plastic laminae are bonded together through an adhesive layer positioned therebetween. The following U.S. Pat. Nos. are representative of such disclosures: 4,227,950, 4,246,207, 4,264,156, 4,268,134, and 4,311,762.
Much of the prior research has involved the combination of glass laminae and plastic laminae consisting of diethylene glycol bis(allyl carbonate) resin, a specific thermosetting resin commercially available from PPG Industries, Pittsburgh, Pa. under the trademark CR-39. Bonding therebetween has frequently been accomplished through silicone-and/or urethane-type adhesives. Those products have encountered optical problems resulting from uneven layers of adhesive and/or glass, and/or structural problems of delamination when subjected to temperature cycling and/or to high humidities.
Therefore, the overall objective of the present invention was to fabricate laminated composite lenses from laminae of inorganic glass and organic plastic which provide optical quality transmission and are free from the structural problems which have plagued such composite lenses in the past.